Generally, the basic steps of processing a color photographic material are a color development step and a desilvering step. In the color development step, the silver halide imagewise exposed is reduced to silver by a color developing agent, and the oxidized color developing agent reacts with a coupler to give a dye image. In the subsequent desilvering step, silver formed in the color development step is oxidized by the action of an oxidizing agent (usually called a bleaching agent), and thereafter dissolved by a complexing agent for silver ions generally called a fixing agent. By going through this desilvering step, only the dye image is formed in the color photographic material.
The desilvering step is carried out by using two baths, i.e., a bleaching bath containing an oxidizing agent and a fixing bath containing a silver ion complexing agent, or a monobath called a bleach-fix bath (blix bath). The present invention is applicable to a two-bath system comprising the bleaching bath and fixing bath.
The actual development process includes, in addition to the basic steps, various auxiliary steps for maintaining the photographic and physical quality of the image, improving the stability of the image, etc. Such additional steps are carried out by using a hardening bath, a stop bath, an image stabilizing bath, a water washing bath, etc.
Ferricyanides, bichromates, ferric chloride, ferric salts of aminopolycarboxylic acids, persulfates, etc. are generally known as the bleaching agent.
The ferricyanides and bichromates, however, give rise to a pollution problem because of the cyanides and hexavalent chromium, and special processing equipment is required for their use. Ferric chloride may form iron hydroxide or stains in the subsequent water washing step, and causes various troubles in practice. The persulfates have the disadvantage that because of their very weak bleaching ability, a very long period of time is required for bleaching. A method has been proposed in this regard to increase their bleaching action by using bleach accelerators. However, the persulfates themselves are designated as a dangerous material under the Fire Prevention Law, and various measures are required for their storage. Generally, therefore, it is difficult to use the persulfates in actual practice.
Ferric salts of aminopolycarboxylic acids (particularly, ferric salt of ethylenediaminetetraacetic acid) have little likelihood of causing pollution, and give rise to no storage problem unlike the persulfates. Thus, they are by far the most widely used bleaching agents at present. However, the bleaching power of the ferric salts of aminopolycarboxylic acids is by no means sufficient. The use of these ferric salts of aminopolycarboxylic acids as bleaching agents can achieve the desired purpose in bleaching or bleach-fixing processing of low-speed silver halide color photographic materials composed mainly of silver chlorobromide emulsions. They have the disadvantage of causing incomplete desilveration or requiring long periods of time for bleaching when they are used for processing high-speed color photographic material which contain silver chlorobromoiodide or silver iodobromide emulsion as a main component and are spectrally sensitized, particularly color reversal photographic materials or color negative photographic materials for photographing, each containing silver halide emulsion having a high silver content.
It has been strongly desired to increase the bleaching power of bleaching baths containing the ferric salts of aminopolycarboxylic acids and to achieve bleaching sufficiently and within short period of time even on color photographic materials of high-speed and a high silver content. To increase their bleaching power, it has been proposed to add various bleach accelerators to the bleaching bath.
Examples of the bleach accelerators proposed include the various mercapto compounds described in U.S. Pat. No. 3,893,858, British Pat. No. 138,842, and Japanese Patent Application (OPI) No. 14623/78, the compounds containing a disulfide bond described in U.S. Pat. No. 4,169,733 (corresponding to Japanese Patent Application (OPI) No. 95630/78), the thiazolidine derivatives described in Japanese Patent Publication No. 9854/78, the isothiourea derivatives described in U.S. Pat. No. 4,144,068 (corresponding to Japanese Patent Application (OPI) No. 94927/78), the thiourea derivatives described in U.S. Pat. Nos. 3,617,283 and 3,809,563 (corresponding to Japanese Patent Publication Nos. 8506/70 and 26586/74, respectively), the thioamide compounds described in British Pat. No. 1,394,357 (corresponding to Japanese Patent Application (OPI) No. 42349/74, and the dithiocarbamates described in Japanese Patent Application No. 26506/80.
Of the above bleach accelerators, the thiourea derivatives, thioamide compounds and dithiocarbamates do not have a sufficient bleach accelerating effect and cannot achieve the purpose of expediting the bleaching step.
The isothiourea derivatives, in many cases, require the copresence of sulfites in order to exhibit their effect sufficiently, and have the disadvantage of not producing an entirely satisfactory effect when added directly to bleaching baths comprising the ferric salts of aminopolycarboxylic acids.
Some of the thiazolidine derivatives have a substantially sufficient bleach accelerating effect, but are difficult to use in practical applications because of their high cost.
The compounds having a mercapto group or a disulfide bond, particularly aminoalkylene thiols and their disulfides, have a substantially sufficient bleach accelerating effect as do the thiazolidine derivatives, and are advantageous in practical applications because of their lower cost than the thiazolidine derivatives.
The present inventors studied the bleach accelerating effects of the aminoalkylene thiols and their disulfides from various practical viewpoints, and found that the following serious disadvantage. Specifically, the present inventors examined the effect of the aforesaid bleach accelerators added to a bleaching solution of the ferric salt of an aminopolycarboxylic acid while a color photographic material was continuously processed by an automatic processor. They have found that they showed a superior bleach accelerating effect in the early stage of the continuous processing (i.e., running), but with the progress of the processing, their effect decreased and was finally lost. This decrease in effect occurred in spite of the fact that the bleach accelerator was also added to a replenisher for bleaching solution, and the replenisher for bleaching solution was added in amounts usually considered suitable. This demonstrates the infeasibility of the above bleach accelerators.